January 18, 2024 | UR Gate

Estimation of the Total Concentration of Positive Ions in Tap Water using Ion Exchange Method

Introduction

Water is essential for every cell and tissue in living organisms, serving as the medium in which all vital processes occur inside and outside cells. The increase in population growth in the Arab Maghreb region, in general, has led to an increase in water consumption, resulting in a decline in the primary reserve of freshwater and its inability to meet essential water needs. This has led to the use of small stations to treat groundwater to make it more suitable for human consumption. The quality of groundwater can be determined through its basic chemical components, and the results of chemical water analysis help determine its suitability as a source for drinking and other purposes. United Nations reports have indicated that the use of polluted and unhealthy water leads to the death of a child every 8 seconds due to water-related diseases. The reports also highlight that 50% of the population in developing countries suffer from water-related diseases, with approximately 80% of all diseases in these countries attributed to water pollution. Moreover, more than 16% of the world's population uses contaminated water.

Ion Exchange

The quality of groundwater can be determined through its basic chemical components, and the results of chemical water analysis help determine its suitability as a source for drinking and other purposes. United Nations reports have indicated that the use of polluted and unhealthy water leads to the death of a child every 8 seconds due to water-related diseases. The reports also highlight that 50% of the population in developing countries suffer from water-related diseases, with approximately 80% of all diseases in these countries attributed to water pollution. Moreover, more than 16% of the world's population uses contaminated water.

Ion Exchange Principle:

Ion exchange relies on the principle that the binding strength of ions to the ion exchanger increases with the ion's charge and size. For example, sodium ion (Na+) can be displaced in an ion exchanger by calcium ion (Ca2+), and when aluminum ions (Al3+) are introduced, they replace calcium ions by binding more strongly.

An ion with strong binding affinity displaces a weakly bound ion from the ion exchanger material. Therefore, it is crucial to select an ion that we want to remove from the solution, which has a stronger binding affinity than the ion already bound to the ion exchanger.

To achieve this, other factors also play a significant role, such as the pH value in the solution, the number of binding sites in the ion exchanger material, the type of ion exchanger, and the concentration of substances.

Theoretical Background

Ion exchange is defined as a process where ions of a solid, insoluble substance are exchanged with ions of a similar charge present in the solution surrounding the solid substance (ion exchanger). Many materials possess ion exchange properties and are used as ion exchangers in analytical chemistry. Initially, natural silicates known as zeolites, synthetic silicates called zeolites, and also activated carbon were used for this purpose. However, the use of these natural materials has become less common due to their low exchange capacity and susceptibility to certain chemicals.

In 1935, scientists Adams and Holme introduced loading resins that carry a replaceable ion-exchangeable group. These resins exhibited suitable properties, leading to their rapid spread and utilization in the field of analytical chemistry.

Each ion exchanger consists of a structural network with binding groups, each linked to an oppositely charged ion (counterion). This ion is then replaced by other ions similar in charge found in the solution surrounding the ion exchanger.

Ion exchangers are classified into positive and negative ion exchangers. A positive ion exchanger can replace positive ions in the solution with positively charged ions associated with its active groups. Positive ion exchangers are either strong, containing the sulfonic group (–SO₃H+) and fully ionized, or weak, containing the carboxyl group (–COO-H+) and partially ionized.

The Explanatory Equations of Ion Exchange Processes

Where: R represents the lattice structure, Mn+ is the ion of the element intended for exchange. As for the negative ion exchanger, it is the exchanger capable of replacing the negative ions in the solution with negative ions associated with its active groups. The resin in this type contains effective basic groups. Negative ion exchangers are classified into strong negative ion exchangers, which carry a tetraamine group R–N+ R3A-, where A- is the replaceable negative ion, and weak negative ion exchangers, which contain a monoamine or a diamine group.

The total concentration of exchanged ions in a solution, such as tap water, can be estimated by passing the solution through a strong positive ion exchanger in its hydrogen cycle –SO-3H+. The positive ions remain or are retained in the positive ion exchanger, while the equivalent amount of hydrogen ions is released into the solution, which can be titrated with a standard base solution. This allows us to determine the total concentration of positive ions. Similarly, the total concentration of negative ions can be estimated by passing a sample of the solution through a strong negative ion exchanger in its hydroxyl form. The negative ions replace the hydroxyl ions, and the liberated hydroxyl ions can be titrated with a standard acid solution.

Sodium Hydroxide:

A strong chemical compound with the chemical formula NaOH, also known as caustic soda (commonly referred to as "atruna" in some Arabic-speaking countries). It is widely used in various industries. Sodium hydroxide has a very high solubility in water, and its aqueous solutions can reach high concentrations. It is considered the primary source in the production of table salt (sodium chloride).

Hydrochloric Acid:

Historically, hydrochloric acid has been known by various names, such as muriatic acid and spirit of salt, as it was obtained from rock salt and green vitriol. It was first prepared by the scientist Jabir ibn Hayyan, and its preparation was described in the writings of Basil Valentine in Europe in the fifteenth century. Andreas Libavius also described it in the sixteenth century, and it was used by chemists like Joseph Priestley, Humphry Davy, and Johann Rudolf Glauber in their research. Glauber later produced it from common salt and sulfuric acid in the seventeenth century. It has various smaller-scale applications, including household cleaning products, gelatin production, food additives, and removing deposits in metal pipes and leather processing.

Handling hydrochloric acid requires extreme caution and appropriate safety precautions, as it is a corrosive liquid. Its salts are called chlorides, and when reacting with organic bases, it forms hydrochloride salts.

Experiment Objective

The study aimed to evaluate the quality of drinking water produced by treatment units in tap water, considering it as the primary source for human consumption within households.

Required Materials:

Strong cationic ion exchanger such as Dowex (Dowax 50w) or Amberlite IR-120.
Hydrochloric acid with a concentration of 0.4M.
Sodium hydroxide with a concentration of 1.0M.
Methyl orange indicator.

Experimental Procedure:

Place the cationic ion exchanger in distilled water for 24 hours to allow the resin beads to swell and the active groups to disperse, facilitating ion flow for positive ion exchange.
Prepare a glass column typically made of glass with a length ranging from 25 to 30 cm. Insert some glass wool into the column and secure it at the bottom as a plug using a long glass rod.
Fill the ion exchange column with distilled water, leaving about 2-3 millimeters above the glass wool plug. Ensure there are no air bubbles inside the column. Lower the cationic ion exchanger into the column until its height reaches 15-20 cm.
If the cationic ion exchanger in the hydrogen cycle does not pass through the column, pass 4M HCl solution through the column at a flow rate of up to 5 milliliters per minute. Repeat the process twice using 25 milliliters of acid each time.
Wash the column with distilled water several times until the ion exchange solution is free of hydrogen ions. Verify this using the methyl orange indicator. Ensure water remains above the exchanger's surface to prevent air bubbles inside, affecting the ion exchange process.
Prepare the model solution in a 250-milliliter volumetric flask. Transfer 25 milliliters of it to the top of the ion exchange column and let it flow at a rate of 5 milliliters per minute. Collect the solution flowing out of the column in a conical flask. Wash the column three times, using 25 milliliters of distilled water each time, and collect the washings in the same conical flask.
Add 5 drops of methyl orange indicator to the collected solution, titrating it with standard sodium hydroxide solution with a concentration of 1.0M until the yellow color appears.
Take the conical flask with its contents and place it under the ion exchange column in the titration until the yellow color appears.
Repeat steps 6, 7, and 8 for two other portions of the unknown solution, each with a volume of 25 milliliters.
To calculate the rate of the sodium hydroxide volume required for titration, and from it, calculate the total concentration of cations in terms of parts per million (ppm) as CaCO3, the following formula is used:

Note:
Laboratory tap water is used as a source for the sample to estimate the total concentration of positive ions.

Discussion and Results

The sodium concentration in the study samples exhibited the lowest reading at 2.48 ppm in sample A and the highest reading at 19.14 ppm in sample D. The average of the readings was 10.87 ppm. The figure below illustrates the sodium concentration in the study samples. It is evident from the figure that the sodium concentration in all study samples is lower than the reference value in the table below. This indicates that the water from the sources of these samples is suitable for human consumption in terms of this parameter.
When comparing the results with locally and imported bottled drinking water in the Kingdom of Saudi Arabia, where the sodium concentration ranges from 14.7 ppm to 51.5 ppm in local brands and from 3.3 ppm to 33 ppm in imported brands, we observe that the maximum sodium concentration in the studied samples is lower than the concentration found in both local and imported bottled drinking water in Saudi Arabia. Additionally, the lowest concentration was also lower than the study's reference values but was close to the imported varieties.

Why is drinking deionized water unsafe?

Aside from the unpleasant taste, a strong buzzing sensation in your mouth, there are valid reasons to avoid drinking deionized water:

Deionized water lacks the minerals usually present in water that provide beneficial health effects. Calcium and magnesium, in particular, are minerals desirable in water.
Deionized water aggressively attacks pipes, container storage materials, filter metals, and other chemicals in water.
Drinking deionized water may increase the risk of metal toxicity, both because deionized water leaches metals from pipes and containers and because hard or mineralized water protects against the absorption of other metals by the body.
Using deionized water for cooking can lead to mineral loss in cooked food.
At least one study found direct damage to the intestinal mucosa from ingesting deionized water. Other studies have not committed to this issue.
There is strong evidence that drinking deionized water disrupts mineral balance. Long-term use of deionized water as drinking water can damage the system, even if additional minerals are present elsewhere in the diet.
There is evidence that distilled and deionized water are less prone to quench thirst.

A- Deionized water may contain pollution in the form of resin exchange ion pieces.
B- While deionized water made from distilled or reverse osmosis pure water may be pure, non-potable deionizing water will not make it suitable for drinking!"

Conclusion

The research results indicate that the water produced in water purification units is suitable for drinking, according to the results of the analyzed parameters included in the study. The sources of these ions in the water samples studied were diverse. This study recommends conducting further research on the water produced in treatment units to include other parameters not covered in the current study. Additionally, it suggests performing necessary analyses on the water sources relied upon by the purification units.

The presence of positive ions in water is beneficial to humans :

Calcium: It is considered one of the major nutrients and is found in bones, teeth, blood, and fluids outside the cell and between cells. The primary function of calcium is to build and maintain bones and teeth. Additionally, calcium plays a crucial role in the metabolic process. Calcium influences the transport function across cell membranes, stabilizes membranes, regulates nerve signals, and helps regulate heartbeats. Calcium concentration in natural water sources, especially groundwater, ranges from ppm 10 to ppm 100. The required daily intake of calcium varies for individuals; children need 210 to 800 mg daily, while men and women need varying amounts. Pregnant and lactating women require up to 1200 mg daily. If the dietary calcium is insufficient, the body withdraws calcium from bone stores, potentially leading to bone loss and osteoporosis, especially during pregnancy and lactation.

Sodium: Sodium is the primary positively charged ion in fluids outside cells and performs essential functions within the human body. These functions include regulating osmotic pressure for body fluids and blood plasma, achieved by balancing water in the body. Sodium also helps maintain the acid-base balance in the body and assists in muscle contraction. In Western Europe and North America, the estimated total daily consumption of dietary sodium chloride is 5-20g, while the estimated total sodium intake is 2-8g. High sodium intake through drinking water can increase blood pressure in newborns.

Potassium: Potassium and sodium share similar functions, with potassium located inside cells in contrast to sodium. Potassium contributes to fluid balance in the body and the transmission of nerve signals. It is an essential element in human nutrition. Both potassium and sodium help maintain normal osmotic pressure within cells. Potassium acts as an assistant to numerous enzymes, is required for insulin secretion, creatinine phosphorylation, and the metabolic processing of carbohydrates and proteins.

Note:
The presence of positive ions in tap water signifies that it is suitable for drinking.

In addition, there are devices that can measure positive ions in water :

To calculate the ionic concentration of potassium and calcium, the BWB XP Flame Photometer, manufactured by BWB Technologies, Newbury, Berks UK, is used. As for the sodium ion concentration, it is measured using the Corning Flam Photometer M410, manufactured by Corning Diagnostics Scientific Instruments, Halsted, Essex, England.